Fire retardant chemicals have been used to impregnate cellulosic-based materials such as plywood, oriented strand board (OSB), and particleboard panels, in order to yield fire-resistant products. However, impregnation with fire retardant chemicals is an expensive procedure and a complicated process, because, in order to be effective, the chemicals must be applied under pressure in a closed pressure cylinder, which requires that a vacuum be pulled first on the load to extract the air from the wood cells prior to pressurization. Furthermore, impregnation of cellulosic materials with fire retardant chemicals adversely affects the long-term structural stability of the cellulosic materials.
Fire retardant coatings have also been used to reduce the surface flammability and improve burn-through resistance of wood products, and other flammable materials. Compositions and uses for fire retardant coatings are discussed further in U.S. Pat. Nos. 5,130,184; 4,818,595; 4,661,398; and 4,572,862, each of which are incorporated by reference in their entireties. Application of fire retardant coatings by brushing, spraying and sheet lamination is known. Brushing or spraying application methods alone, however, can make it difficult to achieve a coating having a uniform thickness and desired surface characteristics. In addition, the coatings may be required to dry or set before additional coatings can be applied in order to build a sufficient volume of material to achieve the desired fire-resistant properties. Application by preparing a separately formed sheet of fire retardant coating material and laminating it to the substrate involves the use of an adhesive layer and has disadvantages related to the process of manufacturing.
Fire retardant coatings can also be used to coat strands of fiber or to impregnate fabrics. Spray-coated strands of chopped fiberglass, for example, may be used as a fire-resistant coating on cellulosic panel substrates, as in the Blazeguard® construction panel product. Suitable fabrics used in fiber impregnation with fire-retardants include, for example: non-woven needled polyester fabrics, non-woven fiberglass or glass-based veil, woven fiberglass, woven carbon cloth, and woven aramid fabric (“Kevlar”). Fabrics of quartz, nylon, or other natural or synthetic or inorganic fibers, woven or unwoven, may also be used. However, the process of impregnating fabric with a fire retardant coating raises challenges. The volume of fire retardant coating impregnated in fabrics can vary, depending on the thickness and porosity of the fabric and the volume and physical qualities of the coating material used to impregnate the fabric. Variations in the volume of the impregnated fabric may affect the effectiveness of the fire retardant coating when the fabric is applied to a flammable substrate. This may make it difficult to consistently produce a product with a desired level of fire resistance.
Because many building products with greater or lesser fire-resistant qualities compete as commodities, production methods used to make such products must be efficient and rapidly scalable in volume. In addition, production methods also need to yield consistent products that meet the standards of the applicable building code.
It is an object of the present invention to provide a system and method for efficiently coating substrates with fire retardant materials in which the dimensions and/or volume of the coating is controlled while yielding a fire-resistant product that maintains a high degree of structural integrity over time, at high temperatures, and during exposure to high temperatures over extended periods.